Heterogeneous acidic oxides are used extensively in the petroleum and petrochemicals industry to catalyze a variety of hydrocarbon conversions. These conversions include catalytic cracking, hydrocracking, naphtha reforming, benzene alklation, xylene isomerization, catalytic dewaxing, and other conversions.
During use, as is generally known, the catalysts undergo loss of catalytic activity, selectivity, or both. The time required for the activity to decay to the point at which the catalyst is no longer useful may vary from as little as a few minutes, as in catalytic cracking, to several years, as with some versions of naphtha reforming. Some of the factors which affect the aging rate include the nature of the feed, the nature of the catalyst, and process conditions. In general, catalyst deactivation is accompanied by an accumulation of "coke" or organic matter on the catalyst and it was early learned to regenerate deactivated catalysts by burning the organic matter in an oxygen-containing gas.
Catalytic dewaxin is described, for example, in U.S. Pat. Nos. Re. 29,398, 3,852,189 and 3,956,102, the disclosures of which are incorporated by reference herein. U.S. Pat. No. 3,956,102 discloses the regeneration of a dewaxing catalyst by burning the deactivated catalyst in oxygen and reactivating the catalyst by contact with hydrogen for about 24 hours at 400 psig. U.S. Pat. No. 4,358,395, the disclosure of which is also incorporated by reference herein, discloses that a ZSM-5 type catalyst which has undergone controlled precoking and has become deactivated in a methanol conversion process is reactivated at 800.degree. F. to about 1200.degree. F. in an atmosphere containing hydrogen.
Although burning in an oxygen-containing gas and treatment with hydrogen are known to regenerate catalysts, these processes in general require high temperature and are costly. In the case of regeneration with hydrogen, special metallurgy is required. Furthermore, these regenerations often fail to fully restore all of the properties of the virgin catalyst.
In accordance with U.S. Pat. No. 4,550,090, deactivated ZSM-5 obtained from a catalytic dewaxing operation is regenerated by contacting the accumulated organic matter with a source of alkali or alkaline earth metal cations, ammonia or mixtures thereof followed by extraction with an organic solvent. Sources of these cations which are mentioned in the patent are the hydroxides or salts with chlorides, acetates and nitrates being particularly preferred. Carbonates are not mentioned.
U.S. Pat. Nos. 4,559,315 and 4,594,333 disclose increasing the ion-exchange capacity and acid catalytic activity of a ZSM-5 type zeolite by treatment with an aqueous solution of a source of alkali metal cation, particularly preferred sources of such cation being sodium or potassium hydroxide or the sodium or potassium salts of acetic, carbonic or phosphoric acid. Reactivation or a coked, spent zeolite is nowhere disclosed or suggested.
U.S. Pat. No. 4,477,582 (Miale) discloses a process for reactivating a steam-deactivated zeolite catalyst using an aqueous ammonium ion-containing solution. Miale distinguishes his steam-deactivated catalysts from coke-deactivated catalysts and indicates that coke-deactivated catalysts can be readily regenerated by air oxidation. Removal of the coke by oxidation conventionally creates no problems, as recognized by Miale, but during oxidative removal of the coke catalyst activity is frequently lost. It would, of course, be desirable to restore activity to the original level, if possible, but Miale does not indicate that his method is of any utility with coke-deactivated zeolites.
It is an object of this invention to provide a process for carrying out a hydrocarbon conversion process using a reactivated zeolite catalyst which has previously become irreversibly deactivated by the deposition of coke during the conversion process.
It is still a further object of this invention to provide a process for reactivating an intermediate pore size zeolite catalyst, e.g., ZSM-5, which has become irreversibly deactivated in the course of use as a dewaxing catalyst.